1. Field of the Invention
The present invention relates generally to a gyro, and more particularly pertains to a magnetic gyro wheel which incorporates a flexible hub, the hub replacing the normally used gimbal and gimbal bearings for the purpose of allowing the gyro to sense and react to a rate of turn, for use with a rate of turn indicator, a navigational instrument, and, more particularly, as a nautical navigation aid.
2. Description of the Prior Art
Prior art rate of turn indicators have usually consisted of complex gyros having numerous mechanical and electromechanical components. The prior art gyro wheels were comparatively heavy and were meticulously machined from steel or other material such as brass, bronze, lead or other similar material, to a high degree of precision. The wheel was usually an integral part of a motor and because of the high speed required, the motor was usually of the direct current variety with the inherent problems normally associated with brushes and commutators such as burned or stuck brushes, burned, worn, or shorted commutator segments and electrical sparking and arcing. The gyro and motor assembly had to be extremely well balanced dynamically. The need for a constant speed led to complicated and delicate centrifugal-force operated switches that intermittently interrupted or applied electrical power to the motor as needed to maintain a fairly constant speed. The switches were a source of trouble, such as sparking and burning of the switch contacts, wear of critical moving parts, and, along with the brushes, a source of radio interference. It also added to the cost of manufacture. Another serious disadvantage was the fact that power interruptions caused small but sudden changes in the speed of the motor. This speed change caused a noticeable spurious deflection of the indicating device used with the gyro.
Prior art gyro and motor assemblies were mounted in a gimbal ring which permitted one degree of freedom as opposed to a fully gimballed gyro such as is used in a gyro compass. This "one degree of freedom" is the one thing that distinguishes the "rate gyro" from gyros used for other purposes. While a single degree of freedom is attained by the use of a single gimbal mount for the gyro as used in prior art rate of turn indicators thus making an ordinary gyro act as a rate gyro, the gimbal mounting limits the gyro's rate sensing ability to one single axis lying in a single plane. This limitation may be desirable in some cases such as when used for the sensing element of an automatic pilot system for use in rough waters or the like, wherein the gyro may be subjected to rotational forces around several axes at right angles to the gyro spin axis at any given time. The gimbal in this case limits the sensitivity of the gyro to the rotational force acting around a desired reference axis such as a vertical axis through the vessel or other vehicle upon which it is installed. This limitation is neither necessary nor desirable for some other uses of the rate gyro, an example being when used to detect a small rate of turn of a towboat or a ship operating in calm waters.
The gimbal and associated bearings introduced another problem of friction. Any appreciable amount of friction in the gimbal bearings drastically affects the accuracy, sensitivity, and response of the rate of turn indicator. This is especially troublesome in rate of turn indicators used on towboats or on ships when they are being slowly maneuvered in close quarters. Under these conditions a degree of sensitivity, accuracy, and response to very small rates of turn is required that is not encountered in fast, highly maneuverable vehicles such as aircraft and the like.
Another problem with gimballed gyros when used as the sensing element of rate of turn indicators as used in the towboat industry arose from the fact that the instrument is primarily used to help the pilot of the vessel to steer a straight course. Used in this way, the gimbals are nearly always in the zero-rate position and will gradually wear the gimbal bearings in such a way that they will develop some reluctance to move from this position.
This action, however slight, reduces the accuracy of the instrument at or near the zero-rate position and reduces its ability to respond to very small rates of turn. The accuracy of the instrument in the zero-rate area and its ability to respond to extremely low rates of turn are of utmost importance as used on towboats.
Rate of turn information sensed by prior art gyros was usually transmitted to the indicating device such as an electrical meter movement through an electromechanical device attached to the gimbal or through a gear train driven by the gimbal. Both methods introduced an additional amount of friction and further reduced the instrument's ability to respond to a small rate of turn since all friction must be overpowered before the pointer of the indicator can move.
Prior art rate of turn indicators are normally supplied in a package of two or more separate units that are installed by a skilled technician. The units are interconnected by electrical cables and are sometimes remote from each other. In a typical installation the indicator unit would be in the pilot house of a boat. The gyro unit would be located under the pilot house, a storage room, or even, in some cases, the engine room. In some cases an additional motor-generator unit is used to supply the DC power for the gyro unit. This kind of arrangement complicates service problems and increases maintenance cost.
The gimbal in prior art gyros is held in the zero-rate position by a spring or springs when no rate of turn is being sensed and is returned to zero position by the same method after a turn is completed. Spring action is non-linear, and the readout from the gyro unit is inherently non-linear.
Prior art rate of turn indicators are normally based on high-speed, short-lived, aircraft type gyros that for all the reasons heretofore given are, in many respects, unsuitable for use on towboats and ships.
The faults and limitations of prior art rate of turn indicators apply also to the use for which they were designed, for aircraft rate gyros.
The flexible-hub magnetic gyro wheel of the present invention overcomes the disadvantages of the prior art gyros by providing a magnetic gyro wheel in combination with a flexible hub which is least in components, least costly to manufacture, and which is much more accurate in providing gyroscopic information. The flexible hub of the present invention produces a freedom of action around an infinity of axes at right angles to the gyro spin axis, and yet limits the sensitivity to a single plane as does the single gimbal, single-degree-of-freedom rate gyro. The flexible hub makes it possible to select any desired axis lying in a plane at right angles to the spin axis of the gyro simply by positioning the sensing elements (the electric pickup coils) at the proper points around the circumference of the gyro. A plurality of pairs of sensing elements properly positioned would make it possible to electrically select any one of a plurality of axes for examination such as yaw, roll, and pitch. Rates of turn around any one of these axes could be examined individually of their vectorial resultant determined by vectorial addition.